1. Field of the Invention
Embodiments of the present invention relate to a tool holding and conveying chain for holding and conveying tools for use in an auto-tool changer (ATC) mounted in a machining tool such as a machining center. More specifically, embodiments relate to a tool holding and conveying chain adapted so that connecting pins for alternately connecting outer link plates with inner link plates are used as tool pots for removably holding and conveying tools.
2. Related Art
An auto-tool changer mounted in a machining tool such as a machining center often employs a tool holding and conveying chain for holding a numbers of tools and for conveying the tools appropriately to tool replacing positions to replace the tools corresponding to machining to be carried out.
A conventional tool holding and conveying chain, as shown in FIGS. 9 and 10, is adapted so that cylindrical connecting pins 530 (also referred to herein as tool pots 530) for alternately connecting outer link plates 510 with inner link plates 520 are used as tool pots 530 for removably holding and conveying tools (not shown).
In order to insert and remove a tool T into and out of the tool pot 530 securely without causing positional misalignment, the prior art tool holding and conveying chain 500 is provided with holder guides 550 at regions connecting cylindrical connecting pins, i.e., the tool pots 530, with the outer link plates 510 so that the holder guides 550 are fixed on the outer surface of the outer link plates 510 corresponding to an adequate position of the tool pots 530 as shown in FIGS. 9 and 10. Thus, the chain 500 assures that the tool pot 530 does not turn relative to the outer link plate 510, which is prone to occur during when the chain travels a curved path corresponding to a layout of equipment of the auto-tool changer as disclosed in Japanese Utility Model Application Laid-open No. Hei.7-7831 (Whole Pages, Whole Drawings), for example.
Still more, as a prior art tool holding and conveying chain that securely prevents turning of the region connecting the cylindrical connecting pin, i.e., the tool pot, with the outer link plate, similarly to the tool holding and conveying chain 500 described above, there is a chain in which planar portions that fit with each other are formed respectively at an outer circumference of a link plate inserting portion of the tool pot and at an inner circumference of tool pot inserting hole of either an inner link plate or an outer link plate, Japanese Utility Model Application Laid-open No. Sho.63-76437 (Whole Pages, Whole Drawings) for example.
However, the tool holding and conveying chain 500 described above has several disadvantages. Because the chain 500 uses the holder guide 550 and fastening means 560 (composed of a bolt and a nut) to fix the holder guide 550 to prevent turning of the region connecting the cylindrical connecting pin, i.e., the tool pot 530, with the outer link plate 510, there is a possibility that the fastening means 560 will break due to an excessive torque applied when the chain 500 is on a driving sprocket of the auto-tool changer.
The chain 500 also has other cumbersome problems. For example, the number of parts such as the holder guide 550 and the fastening means 560 increases with every link. The outer link plate 510 must be provided with a tap hole and the like to fix those parts to the chain 500. In addition, the burdens of positioning the parts in order to install the holder guide 550 and others is burdensom. Plus, there is a need to maintain and manage the necessary fastening torque.
The latter tool holding and conveying chain (Japanese Utility Model Application Laid-open No. Sho.0.63-76437) exhibits its function of preventing the region connecting the cylindrical connecting pin, i.e., the tool pot, from turning with the outer link plate by forming the planar portions that fit with each other at the outer circumference of the link plate inserting portion of the tool pot and at the inner circumference of the tool pot inserting hole of either the inner link plate or the outer link plate as described above. However, this chain has a problem. Because of the weight of the tool attached to the tool pot and others, the tool pot is eccentrically located vertically, for example, within the tool pot inserting hole of the outer link plate. This causes positional misalignment from a normal mounting position. This positional misalignment from the normal mounting position possibly causes trouble in trying to attach and remove the tool into and out of the tool pot securely and smoothly.
Still more, because the planar portion described above is formed at the region of the hole orthogonal to a center line connecting centers of the tool pot inserting holes, and because the eccentric load caused by the tool pot is generated within the tool pot inserting hole of the outer link plate due to the positional misalignment from the normal mounting position, there is tensile stress in a chain longitudinal direction that is concentrated only to the planar portion without dispersing to the whole circumference of the tool pot inserting hole. Consequently, the long-term durability of the outer link plate cannot be assured.